I am very happy with my Nvidia 9400GT. Its direct successor is the 210 series.
This card is inexpensive but well-rated:
PNY VCGGT5201XPB GeForce GT 520 (Fermi) 1GB 64-bit DDR3 PCI Express 2.0 x16 HDCP
Ready Low Profile Ready Video Card
I would go to PCMech.com before buying.